The name Altair is derived from the Arabic for "The Flying Eagle."
The star is located about 16.7 light-years (ly) away from our Sun, Sol,
in the north central part (19:50:47.00+08:52:05.96, ICRS 2000.0) of
Constellation
Aquila,
the Eagle. Also called Alpha Aquilae, Altair is the
brightest
star in Aquila. It is also the lower left member of the
"Summer
Triangle" of first magnitude stars viewed from the northern
hemisphere, formed with Vega (Alpha Lyrae) at
the lower right, and
Deneb
(Alpha Cygni) at upper right. Altair is readily visible to the naked eye.
With a telescope, an optical companion may be visible.
(See Akira Fujii's color photo of
Altair
-- brightest bluish star at the top center of photo.)

Based on Altair's abundance of iron, the star appears
to be twice as enriched as Sol with elements heavier
than hydrogen ("metallicity"),
(Cayrel
de Strobel et al, 1991, page 306). Not surprisingly,
dust has been detected around this young star
(Kuchner
et al, 1998 -- in
pdf).
According to
Holweger
et al (1999), this dust disk may have developed after
most of the surrounding nebulae of gas has been absorbed or
expelled as a shell of gas from the developing star before
it reached the main sequence.

Altair has the New Suspected Variable designation NSV 24910 and is
unusually bright for its spectral type and so may be becoming
a subgiant star that is beginning to evolve off the main sequence, as
it begins to fuse the increasing amounts of helium "ash" mixed with
hydrogen at its core. Although the star should be only a few
hundred million years old, it is so much bigger and hotter than
Sol that it will exhaust its core hydrogen around only a billion
years and turn into a red giant or Cepheid variable before puffing
away its outer layers to reveal a remnant core as a white dwarf.

Altair has one of the fastest known rotational speeds -- 210
kilometers per second (131 miles per second)-- and so completes
at least one rotation in about 10.4 hours. By comparison, the
rotational speed of Sol is only 25.4 days at its equator. As a
result of the rapid spinning, the star probably has the shape of
a flattened ellipsoid, where the equatorial diameter was
estimated to be
14
percent greater than the polar diameter in 2001.
Useful star catalogue numbers for Altair include: Alp or Alf Aql,
53 Aql, HR 7557, Gl 768, Hip 97649, HD 187642, BD+08 4236, SAO 125122,
FK5 745, LHS 3490, LTT 15795, LFT 1499, and ADS 13009 A.

According to one type of model calculations performed for the
NASA
Star and Exoplanet Database, the inner edge of Altair's
habitable zone is located relatively far from the star at
around 2.177 AUs from the star, while the outer edge lies even
farther out at around 4.475 AUs. The distance from Altair where an Earth-type planet would be
"comfortable" with liquid water is centered around 3.3 AUs --
at the outer reaches of the Main Asteroid Belt's orbital distance in
the Solar System. At that distance from the star, such a planet would
have an orbital period of around 4.7 Earth years. If there is life on
any Earth-type planet orbiting youthful Altair, it is likely to be
primitive single-cell, anaerobic (non-oxygen producing) bacteria under
constant bombardment by meteorites and comets as Earth was for the
first billion years. Since there is unlikely to be free oxygen in the
atmosphere of such a planet, it probably would not have an ozone layer
(O3) although Altair puts out a lot more
hard radiation (especially ultraviolet) than Sol.

Hunt for Substellar Companions

A search for faint companions using the
Hubble Space Telescope
from 1995 to 199 found no supporting evidence for a large Jupiter
or brown dwarf sized object
(Schroeder
et al, 2000). On the other hand, the failure to find large substellar
objects like brown dwarfs or a Jupiter- or Saturn-class planet in a
"torch" orbit (closer than the Mercury to Sun distance) around Altair
-- with even the highly effective radial-velocity methods of Geoff
Marcy and Paul Butler -- bodes well for the possibility of Earth-type
terrestrial planets around this star.

Closest Neighbors

The following star systems are located within 10
light-years of Altair.

Located at the celestial equator, Constellation Aquila, the Eagle, and
Constellation Cygnus, the Swan, were hunted by Hercules. Along with
a third, the Vulture (renamed in later as Constellation Lyra, the Lyre),
the birds comprised one of the tasks (the Stymphalian Birds) of
Hercules. For more information about the stars and objects in this
constellation and an illustration, go to Christine Kronberg's
Aquila.
Another illustration is available at David Haworth's
Aquila.

For more information about stars including spectral and luminosity
class codes, go to ChView's webpage on
The Stars of
the Milky Way.